1. Field of the Invention
The present invention relates generally to prosthetic feet. More particularly, the present invention relates to a prosthetic foot with a plurality of cantilever-springs inter-coupled to have a non-linear force versus deflection relationship and to store more energy together than alone.
2. Related Art
Many individuals have lost a limb for various reasons such as war, accident, or disease. In most instances these individuals are not only able to live relatively normal lives, but are able to lead physically active lives as well. Oftentimes, these individuals are aided in their everyday lives by a prosthetic limb. Prosthetic limbs, or prosthesis, generally provide an artificial limb that simulates the function and natural feel of the lost limb.
With respect to prosthetic feet, the development of functional and natural artificial feet has been pursued for some time. Many designs have attempted to copy the anatomy of the foot, or simulate its natural action, by replacing the bones and muscle with various mechanical components. Other designs have departed radically from mere anatomical copying or mechanical simulation of a natural foot by replacing the entire foot with an energy storage element, such as a spring. In this type of design, as the user steps onto the foot, the user's weight compresses the spring. As the user moves forward, the user's weight comes off the foot and the energy stored in the spring is used to propel the user forward.
In addition to the basic use of a spring in a prosthetic foot, it has been attempted to alter the performance of these energy storing feet in a variety of ways: such as by using multiple springs in various configurations; using bladders or materials disposed between various elements of the foot; and using multiple springs that deflect at different intervals of foot deflection to add resistance.
While each of these variations has added some benefit to the field of energy storing prosthetic feet, they have often met with limitations introduced by the general nature of springs. This is due to the fact that the force stored by springs is often linearly proportional to the distance over which the spring has been stretched or compressed. That is, a unit of displacement of the spring generally results in a substantially constant multiple of the unit of displacement being stored in the spring. Thus, typical prosthetic feet utilizing springs have been limited to storage of energy in the spring in an amount that corresponds to a constant multiple of the distance over which the spring was compressed or stretched. This has resulted in a limited amount of energy being storable in the spring and does not effectively leverage the energy expended by a user of the prosthetic foot.